1. Field of the Invention
The present invention relates to a gas sensor, a gas measuring system using the gas sensor, and a gas detection module for the gas sensor. In particular, the present invention relates to an extremely compact gas sensor which can be attached to gas piping of equipment for manufacturing a semiconductor device by using a highly sensitive gas detection device employable in the semiconductor field, a gas measuring system using the gas sensor, and a gas detection module for the gas sensor.
2. Description of Related Art
Fullerenes are a series of spherical molecules consisting only of carbon atoms, which were discovered by Kroto, et al. in a mass spectrum of cluster beams formed by the laser abrasion of carbon (Kroto, H. W; Heath, J. R.; O'Brien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985, 318, 162).
In the 1990's, the existence of a fullerene as a third crystalline carbon material following diamond and graphite was revealed, and a method of mass producing fullerenes by arcing a carbon electrode was developed (Kratschmer, W.; Fostiropoulos, K.; Huffman, D. R. Chem. Phys. Lett. 1990, 170, 167, and Kratschmer, W.; Lamb, L. D.; Fostiropoulos, K.; Huffman, D. R. Nature 1990, 347, 354).
Since fullerenes were discovered, it has been pointed out that fullerenes have unique optical, electrical, chemical, and mechanical properties. Therefore, fullerenes have been considered for use of such as a highly-sensitive sensitizer, an n-type semiconductor, a scavenger of active oxygens, and a microbearing.
However, since a carbon nanotube (CNT), which is a carbon nanomaterial similar to a fullerene, was discovered in the middle of the 1990's, researchers' interest has been focused on this CNT. Therefore, the basic characteristics of fullerenes have not been understood yet, although more than 20 years have passed since fullerenes were discovered. Thus, further investigation is required.
There are many types of materials which are categorized as materials based on a fullerene, which may be referred to as fullerene-based materials, a detailed explanation of which will be given below. Examples of fullerene-based materials include an endohedral fullerene, a heterofullerene (a compound having a fullerene skeleton, with a portion of the carbon atoms forming the skeleton having been replaced by atoms other than carbon such as nitrogen), a norfullerene (a compound having a fullerene skeleton, with a portion of the carbon atoms forming the skeleton having been removed), fullerene derivatives, and fullerene polymers. Manufacturing methods of most of these materials have not been established yet, and hence properties of these materials have not been clarified.
One of the specific applications of a fullerene material, which is a generic name for fullerenes and fullerene-based materials, is a gas detection device for a gas sensor (see Patent Document 1, for example).
Patent Document 1 discloses a gas sensor using a material containing fullerenes, which enables to detect the oxygen content of at most 1014 atoms/cm3 and the water content of at most 1016 atoms/cm3. The initial conductance of the gas sensor disclosed in Patent Document 1 is 0.1 (ohm cm)−1. When oxygen at atmospheric pressure is introduced to the gas sensor, the conductance falls to 2×10−9 (ohm cm)−1. When the gas sensor after the introduction of oxygen is heated in a nitrogen atmosphere so that the oxygen in the gas sensor is exhausted, the conductance returns to around 0.1 (ohm cm)−1. Namely, Reference 1 discloses that the conductance of the material containing fullerenes reversibly changes.    Patent Document 1: WO2007/029684